In a connection fabric environment, output, or source, paths of a card are connected to input, or destination, paths of another card utilizing serial or parallel crossbar switch technology. Each card in the system has N input paths and M output paths. Each source path can request to send data to a destination path, but it must then wait for the destination path to become available for use. If some other path is using the requested destination path, the source path must wait until the destination path is free. This will block the source path from sending data to any other path until this connection is made and the data is sent. This problem is known as head of line blocking. If the source path has any other data to send to a different destination path, it can't send it even if the different destination path is not busy.
Thus, there exists a need for allowing a source path to make a second request to an alternate destination path if the first request cannot be made immediately due to the first requested destination path being connected to some other source path.